The first week of September—a busy time for those heading back to work and school—has also ushered in a fresh batch of lateral moves throughout the Am Law 100.

And Wilson Sonsini Goodrich & Rosati, a high-powered firm that has seen a number of prominent partners leave its ranks in 2017, saw several rivals swoop in this week to scoop up four partners in the Bay Area. A fifth partner, the son of Wilson Sonsini chairman Larry Sonsini, has also moved on to another family business.

Michael Rubin, co-chair of Wilson Sonsini's privacy and data protection practice, left the firm's headquarters in Palo Alto, California, to join Latham & Watkins as a partner in San Francisco. Wilson Sonsini corporate and technology partners Jon Avina, Calise Cheng and Rachel Proffitt are also poised to depart for Cooley but have not yet been permitted to leave the firm.

Avina and Cheng work out of Palo Alto, while Proffitt is a co-founder of Wilson Sonsini's office in San Francisco's technology-heavy South of Market neighborhood. All three partners—who focus their practices on advising clients in the technology sector—were unavailable to discuss their plans to join Cooley, although the latter's leader confirmed his firm's new additions.

Cooley CEO Joe Conroy (pictured right), a former youth football coach who assumed leadership of his firm nearly a decade ago, was succinct in describing the circumstances keeping all three Wilson Sonsini partners at their soon-to-be-former firm.

“They have accepted offers, been voted in [to the partnership] and given notice to their firm,” Conroy said. “I guess all they have to do now is negotiate their withdrawal.”

Conroy called all three partners critical additions that will enhance Cooley's strategic focus on being a go-to firm for capital markets and corporate work for all kinds of clients operating in the technology industry, be they established companies, startups or venture capital firms.

Cooley's recruitment of Avina, Cheng and Proffitt had been in the planning stages for some time, said Conroy, adding that Robert Brigham, a longtime Cooley partner who joined legal recruiting giant Major, Lindsey & Africa as a managing director in 2011, helped broker at least one of the Wilson Sonsini partner moves to the firm.

Conroy noted that it is unusual for Cooley to make such a major lateral acquisition late in the fiscal year, when such hires are often more expensive to a firm's bottom line. But the opportunity to pick up such a talented team—all three departing Wilson Sonsini partners have advised on dozens of notable technology transactions—was one Cooley had to seize.

“They are next generation leaders,” Conroy said of Avina, Cheng and Proffitt, the latest new hires in what has been a busy year for Cooley in the lateral market. “But they are also very loyal, and they engaged in a thoughtful, deliberative process before [deciding to leave].”

In a statement, Wilson Sonsini COO Courtney Dorman addressed the pending departures of the trio destined for Cooley, as well as others that have recently left the firm.

“It is always disappointing to see colleagues and friends leave the firm. That said, everyone has a unique set of circumstances that go into the decision-making process, and we are respectful of that,” she said. “Transitions and mobility are simply a reality in this business. The firm is well-positioned and having an incredibly strong year in all respects. As always, we are extremely proud of our people, our clients and our performance and will continue to grow in all areas of strategic importance to the firm and our client base. We, too, are investing in others.”

Wilson Sonsini welcomed to its ranks last week Elizabeth George, a former deputy general counsel at the U.S. Department of Defense who joined the firm as of counsel for its data protection and privacy practice in San Francisco. That group was led until recently by Rubin, who on Tuesday officially joined Latham's office in the city.

Rubin cited Latham's global platform and cross-jurisdictional expertise as enticing him to leave Wilson Sonsini, a firm he joined a decade ago from Perkins Coie. A legal recruiter whom he would not name—Rubin also declined to discuss any other Wilson Sonsini partners leaving the firm—helped put him in touch with Latham, where he will focus his client work on litigation and regulatory defense in the data privacy space.

In March, Latham recruited former Wilson Sonsini co-managing partner John “Jack” Sheridan as a partner for its emerging companies practice in Silicon Valley. Sheridan declined to comment Wednesday, but in July, Latham also picked up emerging companies partner Page Mailliard, a former Wilson Sonsini partner who left the firm three years ago to care for a family member.

Sheridan's departure was followed by the loss of Brussels antitrust partners Michael Rosenthal and Götz Drauz to Sullivan & Cromwell; at least a half-dozen life sciences litigators to Morrison & Foerster in San Francisco; former national security practice head Donald Vieira to Skadden, Arps, Slate, Meagher & Flom in Washington, D.C.; and three corporate technology partners—Adam Dinow, Sacha Ross and Robert Sanchez—who joined Cooley in New York and the nation's capital.

Another individual with ties to Cooley and no longer at Wilson Sonsini is Larry Sonsini's son, Matthew Sonsini, who returned to the firm in early 2016 after eight years away. Matthew Sonsini's Wilson Sonsini biography page, which archived internet records show was live on the firm's website as of Sept. 1, disappeared this week.

A phone call to Matthew Sonsini at Wilson Sonsini in Palo Alto confirmed that he was no longer listed in the firm's employee directory. An email to the younger Sonsini inquiring as to his status at Wilson Sonsini went unreturned by the time of this story. Matthew Sonsini's profile on professional networking website LinkedIn lists him as a founder and managing partner at an investment fund called Ravello Capital and as chairman of the investment committee at The Sobrato Organization, a privately held real estate development firm based in Cupertino, California.

Matthew Sonsini's father-in-law is John Sobrato, a billionaire real estate developer. The younger Sonsini first left Wilson Sonsini in 2008 to serve as an executive vice president at The Sobrato Organization, where he is currently listed on the company's website as holding several executive-level roles. Lisa Sobrato Sonsini, Matthew Sonsini's wife, is a board president and trustee at the company. She is also an attorney who once worked at now-defunct Brobeck, Phleger & Harrison.

Dorman, Wilson Sonsini's COO, said that Matthew Sonsini actually left the firm for a second time several months ago to return to The Sobrato Organization. “We were certainly disappointed to see him go but completely understand,” Dorman said.

In an odd twist of fate, Matthew Sonsini actually began his career at Latham and then moved to Cooley, where he made partner until leaving the firm to join Wilson Sonsini for the first time in 2001. Cooley topped Wilson Sonsini in the most recent Am Law 100 rankings, taking in $974 million in gross revenue last year, compared with the $755 million earned by Wilson Sonsini in 2016.